1. Field of the Invention
The present invention relates to torque-applying devices and, in particular, to electronic torque wrenches of the type which have a battery-powered torque-sensing circuit and output indicator means.
2. Description of the Prior Art
A standard electronic torque wrench includes a rigid elongated body having a tool end adapted to be rotationally fixed to a part to which a predetermined torque is to be applied, and a handle end. Transducers including strain gauges connected between the tool end and the body generate an actual-value electrical torque signal corresponding to the actual torque being applied by the wrench to the part rotationally coupled to the tool end. Typically, an output circuit provides to the user an indication of the actual torque value being applied and/or a signal that the applied torque equals the predetermined desired torque level.
Such torque wrenches are subject to inaccuracies in use. In the event the output indication is of the actual torque being applied, the user must very carefully watch the indication to avoid inadvertently going past the desired torque. The user must also exercise great care if the output indication is a signal indicating that the predetermined torque value has been reached. Otherwise, since the user is typically applying considerable force to the handle of the wrench, his reaction time will not permit him to relieve that force quickly enough after the signal to avoid overshooting the predetermined torque level.
It is known to provide a warning indication when the applied torque reaches some fixed threshold level below the predetermined desired torque level to give the user time to decrease the applied force before the predetermined level is reached. But for different users and different applications, the rate at which the torque is applied may vary considerably and a threshold level which is appropriate to provide adequate warning for one torque application rate may be inadequate at a faster torque application rate.